Production of dicarboxylic acid esters of alpha-hydroxycarboxylic acid esters



2,712,025 Patented June 28, 1955 PRODUCTION OF DIQARBOXYLIC ACID ESTERS F ALPHA-HYDROXYCGX- YLIC ACID ESTERS Chessie E. Rehberg, Glenside, Pa., and Qharlcs H. Fisher, New Orleans, 1a., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application September 26, 1951, Serial No. 248,440

1 Claim. (Cl. 260347.4)

(Granted under Title 35, U. S. Code (I952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes throughout the world, without the payment to us of any royalty thereon.

This invention relates to plasticizers and especially those produced by esterifications in which a diester is formed by reacting a dicarboxylic acid with a monohydric alcohol ester of an alpha-hydroxycarboxylic acid to esterify both carboxyl groups of the dicarboxylic acid. These esterifications are conventionally carried out by heating a mixture of the dicarboxylic acid and the alphahydroxycarboxylic acid ester in the presence of an acid catalyst.

The reaction is illustrated by the following reaction equation:

OOOE I? COOCHOOOR 26 ZCHOHCOOR i]( 21120 COOH COO HOOOR dicarboxester of a-hydroxy- R ylic acid carboxylie formed diester (IDOOH ester of alpha-hydroxy Ecarboxylic acid 11 being an integer of at least 2.

The formed monohydric alcohol ROI! and formed polyester are thus also available for reaction with the dicarboxylic acid so that in addition to the desired diester, significant amounts of esters corresponding to the following formulas are produced as byproducts:

polyester of alpha-hymonohydric droxycarboxylic acid alcohol dooR (Jooondoon yp p R R C(JOJJHCOOR CO 0( JHCO:lOR I'( it ('JOOCHCOOCHCOOR 30 OCHOO OR B R l I 1.

(Type III) (Type IV) The formation or these several byproduct esters results in lowering the yield of the desired diester and renders purification of the reaction products to obtain a composition of high percentage in the desired diester more diflicult, so that it is desirable for economic reasons to limit formation of undesirable byproduct esters and to limit purification as much as feasible without rendering the final composition unsatisfactory for an intended purpose.

Where the final composition is used as a plasticizer, the presence of the Type I byproduct ester is objectionable because of the relatively high volatility of such ester, and if X or R are long hydrocarbon chains, its poor compatibility with synthetic plastics. Byproduct esters of Types It and Ill are usually efiicient plasticizers, and their presence is not objectionable. The presence of the Type IV byproduct ester is sometimes undesirable because of the relatively low plasticizing efiiciency of such ester, though this is in some instances offset by its high compatibility and low volatility.

In general, according to the present invention, formation of the Type I and Type 1V esters is suppressed thus to obtain a higher yield of the desired diester. Suppression of Type I ester formation is accomplished by addition of the Type I ester to the reaction mixture and of the IV ester by addition of the ROH alcohol. If it is desired to suppress formation of both Type I and Type IV esters, the esterification can be' conducted in presence of both the added Type I ester and the ROI-I alcohol.

The invention is exhibited in specific detail by the following examples:

Example I A control was first run according to the following procedure:

Two moles of butyl lac.ate (R=butyl), one mole of adipic acid (X=(CI-I2)4), and 1.0 g. of concentrated sulfuric acid were dissolved, refluxed in a still having a 2- foot fractionating column with a water trap and reflux condenser at its top. Water was withdrawn intermittently during 5 hours of refluxing, after which the esterification was substantially complete. The product was washed with dilute sodium carbonate solution and water until neutral.

The residue was then purified by heating to C. under a pressure or" 0.1 mm. to remove water and other volatile impurities. The neutral, odorless, light-colored, oily product thus obtained (n 1.4440, di 1.055), was compatible with and suitable as a plasticizer for polyvinyl chloride, cellulose acetate and ethyl cellulose.

Distillation of this product showed it to consist primarily of bis-(butyl lactate) adipate and butyl (butyl lactate) adipate as well as polylactic esters of ipic acid, present in amounts corresponding to about 0.3, 0.3, and 0.2 mole, respectively, of the adipic acid used in the re action. The polylactic esters portion of the product consisted mainly of (butyl lactate) (butyl lactyllactate) adipate and bis-(butyl lactyllactate) adipate.

Following the foregoing procedure, two moles of butyl lactate was reacted with one mole of adipic acid. How ever, in this case varying amounts of butyl adipate were added to the initial reaction mixture. In each instance essentially the same relative yield of the reaction products a was obtained as in the control procedure. Formation of butyl adipate in the reaction, however, was suppressed in proportion to the amount of added butyl adipate. Thus, the addition of 0.25, 0.37, and 0.50 mole of butyl adipate to the reaction mixture resulted in the formation of 0.2, 0.1, and 0.07 mole of butyl adipate, respectively, in the course of the esterification process. An initial mixture of reactants consisting of two moles butyl lactate, one mole of adipic acid, and one mole of butyl adipate yielded a reaction product containing only 0.7 mole of butyl adipate.

Following the foregoing control procedure, two moles of butyl lactate was reacted with one mole of adipic acid in the presence of varying amounts of butanol added to the initial reaction mixture. In each case essentially the same total yield of the reaction products was obtained as in the control procedure. Formation of the polylactic esters of adipic acid, however, was repressed by the addition of butanol to the reaction mixture. Thus the addition of 1 mole, and 2 moles of butanol to the reaction mixture resulted in a final product containing the polylactic esters of adipic acid in amounts corresponding to 0.08 and 0.03 mole, respectively, of the adipic acid used in the reaction.

Example II A control was run according to the following procedure:

Five moles of capryl lactate, 2 moles of sebacic acid and g. of p-toluene sulfonic acid were mixed and refluxed as described in Example I, the temperature in the pot not being allowed to exceed 140150 C. In 3 hours 76 cc. of water was removed and the esterification was substantially complete. The catalyst was neutralized by addition of 35 g. of powdered anhydrous sodium carbonate and stirring for 1 /2 hours.

The product was then filtered, volatile material was removed by heating to 175 C. at a pressure of 0.10.2 mm. and the residue was treated with decolorizing charcoal. The neutral odorless, light-colored, oily product thus obtained (12 1.448, d4 0.970) was an excellent plasticizer'for polyvinyl chloride and ethyl cellulose.

Distillation of this product sl1owed.that it consisted of bis(capryl lactate) sebacate containing some capryl sebacate and mixed esters formed by esterification of sebacic acid with capryl polylactates.

Formation of capryl sebacate, and of the polylactic esters of sebacic acid, was repressed on addition of capryl sebacate and of capryl alcohol, respectively, to the initial reaction mixture, in a manner analogous to that described in Example I, in connection with suppression of butyl adipate, and butyl polylactate adipates formation in the esterification of adipic acid with butyl lactate.

Example 111 Following the procedure of Example I, two moles of 5 butyl lactate was reacted with 1 mole of sebacic acid. The reaction product so obtained was light colored, oily liquid (n 1.448, d4 1.024) highly compatible with polyvinyl chloride and ethyl cellulose. This product was found to consist mainly of bis(butyl lactate) sebacate, containing some butyl sebacate and sebacic acid esters of butyl polylactates.

The formation of butyl sebacate and of the polylactic esters in this esterification process was repressed by addition of butyl sebacate and of butanol, respectively, to the initial reaction mixture, in a manner analogous to that described in Example I in connection with the corresponding esters of adipic acid.

Similar results were obtained essentially by the procedures of the above examples on using corresponding amounts of other dibasic acids such as phthalic, maleic, fumaric, citraconic, itaconic, or succinic in place of adipic or sebacic acid, and other esters of alpha-hydroxycarboxylic acid, like methyl, ethyl, see-butyl, octyl, Z-ethylhexyl, 2-chloroethyl, allyl, Z-methallyl, 2-chloroallyl, 2-

ethoxyethyl, 2-butoxyethyl, 2-n-hexyloxyethyl, 2-(2- butoxyethoxy) ethyl, or tetrahydrofurfuryl lactate, glycolate or alpha-hydroxy-isobutyrate in place of the lactic esters utilized in the above examples. The characteristics of some of the esters so obtained are shown in the following table wherein lactates (R=CI-Iz) are the esters of alpha-hydroxycarboxylic acid used in each procedure.

TABLE Diearboxylie Acid R 7111 d4 Adipic" I. 1075 D 1. 0543 D 0. 9960 Do 0. 9997 D0- 1. 0574 D0 1. 1085 Do. 2-Butoxyethyl. 1. 4472 1. 0668 Do- 2-n-Hexyloxyethyl 1. 4490 1. 0327 Do 2-(2Butoxyethoxy) ethy1. 1. 4507 1. 0725 Do Tetrahydroturiuryl 1. 4680 1. 1677 Phthalic .d0 1- 5030 1. 2188 D 2(2-Butoxyethoxy) ethyl 1. 4790 1. 1130 Do Z-Ethoxyethyl l. 4859 1. 1622 Do All 1. 5000 1. 1725 D0 1. 5156 1. 2964 Maleic 1. 4646 1. 0935 D 1. 4498 1. 2076 D0 1. 4478 1.1510 D0- 1. 4600 1.1224 Fumaric... 1. 4650 1.1323 Sebaeia. 1. 4051 1. 1706 D 1. 4465 1. 0200 Do 1. 4452 1.0540 D0- 1. 4475 9740 D0 1. 4506 0. 0782 C1traconie 1. 4548 1. 0840 Itaconic. 1. 4580 1. 0987 Succiuic 1. 4375 1. 1344 D l. 4400 1. 0714 D0 1. 4460 1. 0042 D0 1.4408 1.1925 D0 1.4554 1.1353

Phthalate of allyl gly- 1. 5162 1. 2300 colate.

Other esterification catalysts such as hydrogen chloride or benzenesulfonic acid can be used in lieu of sulfuric acid and toluene sulfonic acid, and toluene or other entraining agents may be used to aid in removal of water during esterification. In the preparation of all these products, the amount of the corresponding alcohol ester of the dicarboxylic acid, and of the esterification products of the dicarboxylic acid with the poly-(hydroxymonocarboxylic acid) esters, formed in the reaction can be repressed by conducting the process in the presence of the corresponding alcohol ester of the dicarboxylic acid and of the corresponding alcohol, respectively, essentially as described in the foregoing examples in connection with the repression of butyl adipate and of the butyl polylactate esters of adipic acid.

We claim:

Plasticizers produced according to the following reaction equation:

l (IIOOH R COOCHCOOR X +2CHOHCOOR 21120 OOH OOCHCOOR being selected from the group of acids consisting of aliphatic dicarboxylic acids having not more than 10 carbon atoms, and phthalic acid, R being a monovalent organic radical of not more than 8 carbon atoms selected from the group consisting of alkyl, chloroalkyl, alkoxyethyl, alkenyl, chloroalkenyl, and tetrahydrofurfuryl radi- 5 6 cals, and R being selected from the group consisting of being also produced, suppressing the amount of the type H and alkyl, byproduct esters having the formulas I byproduct ester produced by addition to the reaction 000R 000R mixture of an ester having the same formula as the type X C I ester, and suppressing the amount of the type IV byr product ester produced by addition to the reaction mixture 10 o R (1J0 0 CH0 0 O R of an alcohol having the formula ROH.

(Type D (Type II) References Cited in the file of thls patent UNITED STATES PATENTS O o O E 0 OR 0 g 1 10 2,260,295 Carruthers et a1. Oct. 28, 1941 v I n 2,449,001 Mikiska Sept. 7, 1948 fi 2,452,209 Rehberg et al. Oct. 26, 1948 oooonooot lnooon 00[o 3Ho0]0R 2,534,255 Filachione et a1 Dec. 19, 1950 I R! R! (wherein 'n is an integer of at least 2) 15 yp yp 

